Top contact LED thermal management

ABSTRACT

An LED having enhanced heat dissipation is disclosed. For example, an LED die can have extended bond pads that are configured to enhance heat flow from an active region of the LED to a lead frame. A heat transmissive substrate can further enhance heat flow away from the LED die. By enhancing heat dissipation, more current can be used to drive the LED. The use of more current facilitates the production of brighter LEDs.

TECHNICAL FIELD

The present invention relates generally to light emitting diodes (LEDs).The present invention relates more particularly to methods and systemsfor providing thermal management for LEDs.

BACKGROUND

Light emitting diodes (LEDs) are well known. LEDs are semiconductordevices that emit light when the p-n junction thereof is forward biased.LEDs are commonly used as indicator lights on electronic devices. Forexample, the red power indicator on consumer electronic devices is oftenan LED.

The use of LEDs in higher power applications is increasing. For example,LEDs are being used in applications such as flashlights, displays, andarea lighting. However, the brightness of an LED is limited, as least inpart, by the ability of the LED to dissipate heat. Brighter LEDs requireincreased current. Increased current inherently results in increasedheating of the LED.

As an LED gets hotter, its efficiency decreases. Thus, in order to takeadvantage of the increased current, the heat resulting therefrom must bemanaged, e.g., removed from the LED. Excessive heat also reduces thelife of an LED.

In view of the foregoing, it is desirable to provide a method and systemfor managing heat in LEDs and the like.

BRIEF SUMMARY

Methods and systems for managing heat from a light emitting diode (LED)are disclosed herein. These methods and systems can provide enhancedheat dissipation for LEDs and the like. For example, in accordance withan example of an embodiment an LED die can comprise extended bond padsthat are configured to enhance heat flow from an active region of theLED to a lead frame. Heat can then flow from the lead frame to a heattransmissive substrate, from which the heat can be radiated into the airand/or conducted to another structure.

According to an example of an embodiment, an LED die can comprise asubstrate, a layer of n-type material formed upon the substrate and alayer of p-type material formed upon the substrate. The p-type materialcan cooperate with the n-type material to define an active region. Atleast one bond pad can be formed upon the n-type material and/or thep-type material. The bond pad can be configured to facilitate attachmentof the LED to a lead frame. Further, the bond pad can be configured tofacilitate heat flow from an active region of the LED to a lead frame.For example, the bond pad can be extended or enlarged with respect tocontemporary bond pads.

According to an example of an embodiment, an LED assembly can compriseat least one die, a lead frame, and at least one bond pad formed uponthe die. The bond pad can be configured to facilitate attachment of thedie to the lead frame. Further, the bond pad can be configured tofacilitate heat flow from the die to a lead frame.

According to an example of an embodiment, a method for forming an LEDdie can comprise forming extended bond pads upon at least one of ap-type material and an n-type material. The bond pads can be configuredto enhance heat flow from an active region of the LED to a lead frame.

According to an example of an embodiment, a method for fabricating anLED die can comprise providing a substrate, forming a layer of n-typematerial upon the substrate, and forming a layer of p-type material uponthe substrate. The p-type material can cooperate with the n-typematerial to define an active region. At least one bond pad can be formedupon the n-type material and/or the p-type material. The bond pad can beconfigured to facilitate attachment of the LED to a lead frame. Further,the bond pad can be configured to facilitate heat flow from an activeregion of the LED to a lead frame.

According to an example of an embodiment, a method for fabricating anLED assembly can comprise providing at least one die and attaching thedie/dice to a lead frame via a bond pad formed upon the die/dice. Thebond pad can be configured to facilitate heat flow from the die to alead frame.

By enhancing heat flow from the LEDs, brighter LEDs can be provided.These brighter LEDs can be used in such applications as flashlights,displays, and area lighting.

This invention will be more fully understood in conjunction with thefollowing detailed description taken together with the followingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a semi-schematic perspective view of a contemporary lightemitting diode (LED) die, showing the non-enlarged or non-extended bondpads thereof:

FIG. 2 is a semi-schematic top view of an LED die, showing areas intowhich the bond pads (the P-pad and the N-pad) can be enlarged accordingto an example of an embodiment;

FIG. 3 is a semi-schematic top view of an LED die, showing enlargementof the areas of the bond pads according to an example of an embodiment;

FIG. 4 is a semi-schematic side view of a contemporary LED die, showingthe size of the bond pads, such as for comparison to FIG. 5;

FIG. 5 is a semi-schematic side view of an LED die showing an increaseof the area and the height of the bond pads according to an example ofan embodiment;

FIG. 6 is a semi-schematic side view of two LED dice that are positionedfor attachment to a lead frame, wherein the lead frame is attached to atransparent carrier, according to an example of an embodiment;

FIG. 7 is a semi-schematic side view of two LED dice that are attachedto a lead frame, wherein the lead frame is attached to a transparentcarrier as in FIG. 6, and further showing a substrate positioned forattachment to the dice and lead frame, according to an example of anembodiment;

FIG. 8 is a semi-schematic side view of two LED dice that are attachedto a lead frame as in FIG. 6, a substrate positioned attached to thedice and lead frame and showing the transparent carrier removed from thelead frame, according to an example of an embodiment;

FIG. 9 is a semi-schematic side view of two LED dice that are attachedto a lead frame as in FIG. 6, showing phosphors formed atop the dice,according to an example of an embodiment; and

FIG. 10 is a semi-schematic top view of a lead frame layout, accordingto an example of an embodiment.

Embodiments of the present invention and their advantages are bestunderstood by referring to the detailed description that follows. Itshould be appreciated that like reference numerals are used to identifylike elements illustrated in one or more of the figures.

DETAILED DESCRIPTION

Methods and systems for enhancing heat dissipation from LEDs aredisclosed. For example, an LED die can have extended bond pads that areconfigured to enhance heat flow from an active region of the LED to alead frame. A heat transmissive substrate can further enhance heat flowaway from the LED die. By enhancing heat dissipation, more current canbe used to drive the LED. The use of more current facilitates theproduction of brighter LEDs.

According to an example of an embodiment, an LED die can compriseextended bond pads that are configured to enhance heat flow from anactive region of the LED. For example, heat flow from the LED to a leadframe can be facilitated.

According to an example of an embodiment, an LED die can comprise asubstrate, a layer of n-type material formed upon the substrate, and alayer of p-type material formed upon the substrate. The p-type materialcan cooperate with the n-type material to define an active region of theLED. At least one bond pad can be formed upon the n-type material and/orthe p-type material. The bond pad can be configured to facilitateattachment of the LED to a lead frame. Further, the bond pad can beconfigured to facilitate heat flow from an active region of the LED to alead frame.

The bond pads can be formed upon both the n-type material and the p-typematerial. The bond pad(s) can be formed to have approximately equalheight, so as to facilitate attachment thereof to the lead frame. Thebond pads comprise a metal, such as gold.

According to an example of an embodiment, an LED assembly can compriseat least one die, a lead frame, and at least one bond pad formed uponthe die. The bond pad(s) can be configured to facilitate attachment ofthe die to the lead frame. Further, the bond pads can be configured tofacilitate heat flow from the die to a lead frame.

A plurality of dice can be attached to the lead frame. One or more bondpads can be formed upon the n-type material of the die/dice and one ormore bond pads can be formed upon a p-type material of the die/dice. Aheat transmissive substrate can be attached to the die/dice andconfigured to facilitate heat flow away from the die/dice. The heattransmissive substrate can comprise a metal or combination of metals.For example, the heat transmissive substrate can comprise copper oraluminum.

The heat transmissive substrate can be attached to the lead frame andthe die/dice via solder. The die/dice can be disposed generally betweenthe lead frame and the heat transmissive substrate.

According to an example of an embodiment, a method for forming an LEDdie can comprise forming a extended bond pad upon a p-type materialand/or an n-type material. The bond pad(s) can be configured to enhanceheat flow from an active region of the LED to a lead frame.

According to an example of an embodiment, a method for fabricating anLED die can comprise providing a substrate, forming a layer of n-typematerial upon the substrate, and forming a layer of p-type material uponthe substrate. The p-type material can cooperate with the n-typematerial to define an active region. At least one bond pad can be formedupon the n-type material and/or the p-type material. Any desired numberof bond pads can be formed upon the n-type material and/or the p-typematerial. The bond pad(s) can be configured to facilitate attachment ofthe LED to a lead frame. Further, the bond pad(s) can be configured tofacilitate heat flow from an active region of the LED to a lead frame.

According to an example of an embodiment, a method for fabricating anLED assembly can comprise providing at least one die and attaching thedie/dice to a lead frame via a bond pad formed upon the die/dice. Thebond pad can be configured to facilitate heat flow from the die to alead frame.

Referring now to FIG. 1, a contemporary LED die comprises n-typematerial and p-type material formed upon a substrate so as to define anactive region. Current is provided to the active region via wires 11attached to one of the types of material, e.g. the p-type material, andvia wires 12 attached to the other type of material, e.g., the n-typematerial. Current can be distributed to the active region moreeffectively using current spreader or current spreading layers 13 and 14according to well-known principles.

The wires 11 and 12 attach to bond pads 16 and 17. The bond pads 16 and17 of a contemporary die do not facilitate substantial heat flow fromthe active region. Indeed, the bond pads 16 and 17 may, at least in someinstances, inhibit heat flow from the active region of a contemporarydie.

Referring now to FIG. 2, according to an example of an embodiment thepads 16 and 17 can be enlarged so as to extend beyond the area of thedie shown in FIG. 1. For example, the pads 16 and 17 can be enlarged inthe Y direction (both up and down as shown in FIG. 2). The pads 16 and17 can alternatively be extended in the X direction. The pads 16 and 17can be extended in both the X and Y directions. The pads 16 and 17 canbe extended in any desired direction or directions.

In this manner, the pads 16 and 17 can be made more heat transmissive.More particularly, the pads 16 and 17 can be configured to facilitateheat flow from the active region of die 20. For example, the pads 16 and17 can be configured to facilitate heat flow from the active region ofdie 20 to a lead frame as discussed herein.

Referring now to FIG. 3, the pads 16 and 17 have been enlarged in boththe Y and X directions. Pads 16 and 17 have been enlarged to defineextended pads 31 and 32. Extended pads 31 and 32 facilitate electricalcontact between the die and a lead frame.

Extended pads 31 and 32 also facilitate heat flow from the die, e.g.,the active region of the die, to the lead frame. This extension of thepads 16 and 17 facilitates such heat flow by enhancing physical (andthus thermal) contact between the die and the lead frame.

Referring now to FIG. 4, a contemporary die comprises a substrate 41having a layer of n-type material 42 and a layer of p-type material 43formed thereon. For example, the substrate 41 can comprise alumina(Al₂O₃). Those skilled in the art will appreciate that other materialsare likewise suitable.

For example, the p-type material 43 can comprise p-doped galliumarsenide (GaN) and the n-type material 42 can comprise n-doped GaN.Those skilled in the art will appreciate that other materials arelikewise suitable.

A p-pad 16 is formed on the p-type material 43 so as to facilitatecurrent flow to the p-type material 43. An n-pad 17 is formed on thesubstrate 41 so as to facilitate current flow to the n-type material 42.Wires (such as wires 11 and 12 of FIG. 1) are wire bonded to the p-pad16 and the n-pad 17.

A reflector 46 can be formed to the bottom of the substrate 41. Forexample, the reflector can comprise gold. Those skilled in the art willappreciate that other materials are likewise suitable.

The upper surface of the layer of p-type material 43 and the sidesurfaces of the layer of p-type material 43 and the layer of n-typematerial 42 have a layer of silicon dioxide (SiO₂) formed thereon.

The top of the p-pad 16 and the top of the n-pad 17 are at differentheights in this contemporary LED die. The top of the p-pad 16 has aheight of Dimension A and the top of the n-pad 17 has a height ofDimension B. Dimension A and Dimension B are substantially differentfrom one another. This difference in height is not important in this LEDdie because it is to be wire bonded, according to contemporary practice.

Referring now to FIG. 5, an LED die 50 having extended pads 31 and 32 isshown in cross-section. The top of extended p-pad 31 and the top ofextended n-pad 32 are at approximately the same height. The top ofextended p-pad 31 has a height of Dimension C and the top of extendedn-pad 32 has a height of Dimension D. Dimension C and Dimension D aresubstantially the same. Wire bonds are not used in this example of anembodiment.

By making the top of extended p-pad 31 and the top of extended n-pad 32have approximately the same height, the die can more readily be attachedto a lead frame (as shown in FIG. 6). That is, the lead frame can begenerally flat and can contact the extended p-pad 31 and the top ofextended n-pad 32.

Referring now to FIG. 6, two dice 50, each having extended pads 31 and32 (as in FIG. 5) are positioned for attachment to a lead frame 61. Thetwo dice 50 each can have extended bond pads 16 and 17. The bond pads 16and 17 can have substantially the same height. The lead frame canfacilitate the flow of heat away from the dice 50.

The lead frame 61 can comprise a thermally conductive material, such ascopper. The lead frame 61 can have a layer of gold applied thereto. Thelayer of gold can be applied to the lead frame 61 on the surfacesthereof that contact extended pads 31 and 32 and/or the layer of goldcan be applied to the lead frame 61 on surfaces thereof that do notcontact extended pads 31. As those skilled in the art will appreciate,such gold layers can both enhance electrical connection of the leadframe 61 to the dice 50 and can enhance the thermal conductivity of thelead frame 61.

The extended pads 31 and 32 of the dice 50 can be attached to the leadframe 61 via fluxless soldering. For example, gold/tin (AuSn) solder canbe used to attach the dice 50 can to the lead frame 61.

The lead frame 61 can temporarily or permanently rest upon and besupported by a transparent carrier 61. Transparent carried 61facilitates handling and processing of the lead frame 61 and attacheddice 50. An alignment camera can be used to align the dice 50 to thelead frame 61 to facilitate attachment of the dice 50 to the lead frame61.

Solder layers 64 can be formed upon the lead frame 61 SO as tofacilitate attachment of the dice 50 thereto. Solder layers 64 cancomprise gold (Au) solder or gold/tin (AuSn) solder, for example.

Reflectors 65 can be formed upon the side walls of the lead frame 61.Reflectors 65 can comprise silver (Ag) or aluminum (Al), for example.Reflectors 65 direct light from dice 50 upward through phosphor 91 (FIG.9).

Referring now to FIG. 7, heat transmissive substrate 71 is positionedfor attachment to the lead frame 61 and/or the dice 50. For example, asolder mask 72 can be applied to the heat transmissive substrate 71 tofacilitate patterning of the heat transmissive substrate 71 with solder.The heat transmissive substrate 71 can be patterned with tin/silver(SnAg) solder, for example. Reflow soldering can thus be used to attachthe thermally transmissive substrate 71 to lead frame 61 and/or the dice50.

Referring now to FIG. 8, the transparent carrier 62 can be detached fromthe lead frame 61. The transparent carrier 62 is generally not needed tosupport the lead frame 61 and the dice 50 after the thermallytransmissive substrate 71 has been attached to the lead frame 61 and/orthe dice 50.

Referring now to FIG. 9, one or more phosphor 91 can be deposited uponthe dice 50 so as to change the color of light emitted thereby.Alternatively, the phosphor(s) 91 can be omitted. One or more lenses canalso be formed to the dice 50.

According to an example of an embodiment, heat from an LED or the likecan readily flow from the device into a lead frame via extended bondpads of the device. Heat can then flow from the lead frame to a heattransmissive substrate. Heat from the heat transmissive substrate can beradiated into the air and/or conducted to another structure. Forexample, heat from the heat transmissive substrate can be conducted intoa fixture, mount, bracket, package, or other structure within or towhich the heat transmissive substrate is mounted.

Referring now to FIG. 10, according to an example of an embodiment alead frame can comprise one or more positive busses 101 and one or morenegative busses 102. The positive buss(es) 101 can alternate with thenegative buss(es) 102. In this manner, current can be provide to the LEDdie 50. Further, heat can be carried away from the dice 50 via thepositive buss(es) 101 and the negative buss(es) 102 of the lead carrier61.

As used herein, the term “active region” can be defined to include aregion in a light-emitting diode where injected electrons and holesrecombine to generate photons in the LED when current is applied.

As used herein “formed upon” can be defined to include deposited,etched, attached, or otherwise prepared or fabricated upon whenreferring to the forming the various layers.

As used herein “on” and “upon” can be defined to include positioneddirectly or indirectly on or above.

As used herein, the term “package” can be defined to include an assemblyof elements that houses one or more LED chips and provides an interfacebetween the LED chip(s) and a power source to the LED chip(s). A packagecan also provide optical elements for the purpose of directing lightgenerated by the LED chip. Examples of optical elements are lens andreflectors.

As used herein, the term “transparent” can be defined to include thecharacterization that no significant obstruction or absorption ofelectromagnetic radiation occurs at the particular wavelength orwavelengths of interest.

As used herein, the term “spreader layer” can be defined to include alayer that spreads current and is separate from the layers in the LEDcore.

By enhancing heat dissipation, more current can be used to drive LEDs.The use of more current facilitates the production of brighter LEDs. Theproduction of brighter LEDs facilitates use in such applications asflashlights, displays, and area lighting.

Further, the use of a lead frame eliminates the need for wire bonds. Asthose skilled in the art will appreciate, the use of wire bondsincreases the cost of packaging LEDs and decreases the yield of thepackaging process.

Embodiments described above illustrate, but do not limit, the invention.It should also be understood that numerous modifications and variationsare possible in accordance with the principles of the present invention.Accordingly, the scope of the invention is defined only by the followingclaims.

1. An LED die comprising extended bond pads that are configured toenhance heat flow from an active region of the LED to a lead frame. 2.An LED die comprising: a substrate; a layer of n-type material formedupon the substrate; a layer of p-type material formed upon thesubstrate, the p-type material cooperating with the n-type material todefine an active region; and at least one bond pad formed upon at leastone of the n-type material and the p-type material, the bond pad beingconfigured to facilitate attachment of the LED to a lead frame and beingconfigured to facilitate heat flow from an active region of the LED to alead frame.
 3. The LED die as recited in claim 2, wherein a bond pad isformed upon both the n-type material and the p-type material.
 4. The LEDdie as recited in claim 2, wherein a bond pad is formed upon both then-type material and the p-type material and the bond pads haveapproximately equal height so as to facilitate attachment thereof to thelead frame.
 5. The LED die as recited in claim 2, wherein the bond padscomprise gold.
 6. An LED assembly comprising: at least one die; a leadframe; and at least one bond pad formed upon the die, the bond pad beingconfigured to facilitate attachment of the die to the lead frame andbeing configured to facilitate heat flow from the die to a lead frame.7. The LED assembly as recited in claim 6, wherein a plurality of diceare attached to the lead frame.
 8. The LED assembly as recited in claim6, wherein a bond pad is formed upon an n-type material of the die/diceand a bond pad is formed upon a p-type material of the die/dice.
 9. TheLED assembly as recited in claim 6, wherein a bond pad is formed upon ann-type material of the die/dice, a bond pad is formed upon a p-typematerial of the die/dice, and the bond pads have approximately equalheight so as to facilitate attachment thereof to the lead frame.
 10. TheLED assembly as recited in claim 6, wherein the bond pads comprise gold.11. The LED assembly as recited in claim 6, further comprising a heattransmissive substrate attached to the die/dice and configured tofacilitate heat flow away from the die/dice.
 12. The LED assembly asrecited in claim 6, further comprising a heat transmissive substrateattached to the die/dice and configured to facilitate heat flow awayfrom the die/dice, wherein the heat transmissive substrate comprises ametal substrate.
 13. The LED assembly as recited in claim 6, furthercomprising a heat transmissive substrate attached to the die/dice andconfigured to facilitate heat flow away from the die/dice, wherein theheat transmissive substrate comprises a copper substrate.
 14. The LEDassembly as recited in claim 6, further comprising a heat transmissivesubstrate attached to the die/dice and configured to facilitate heatflow away from the die/dice, wherein the heat transmissive substratecomprises an aluminum substrate.
 15. The LED assembly as recited inclaim 6, further comprising a heat transmissive substrate that isattached to the lead frame and the die/dice via solder.
 16. The LEDassembly as recited in claim 6, further comprising a heat transmissivesubstrate and wherein the die/dice are disposed generally between thelead frame and the heat transmissive substrate.
 17. A method for formingan LED die, the method comprising forming an extended bond pad upon atleast one of a p-type material and an n-type material, wherein the bondpad(s) are configured to enhance heat flow from an active region of theLED to a lead frame.
 18. A method for fabricating an LED die, the methodcomprising: providing a substrate; forming a layer of n-type materialupon the substrate; forming a layer of p-type material upon thesubstrate, the p-type material cooperating with the n-type material todefine an active region; and forming at least one bond pad upon at leastone of the n-type material and the p-type material, the bond pad beingconfigured to facilitate attachment of the LED to a lead frame and beingconfigured to facilitate heat flow from an active region of the LED to alead frame.
 19. The method as recited in claim 18, wherein a bond pad isformed upon the n-type material and the p-type material.
 20. The methodas recited in claim 18, wherein bond pads are formed upon the n-typematerial and the p-type material so as to have approximately equalheight.
 21. A method for fabricating an LED assembly, the methodcomprising: providing at least one die; and attaching the die/dice to alead frame via a bond pad formed upon the die/dice, the bond pad beingconfigured to facilitate heat flow from the die to a lead frame.
 22. Themethod as recited in claim 21, wherein a bond pad is formed upon ann-type material of the die/dice and a bond pad is formed upon a p-typematerial of the die/dice.
 23. The method as recited in claim 21, whereina bond pad is formed upon an n-type material of the die, a bond pad isformed upon a p-type material of the die/dice and the bond pads areformed so as to have approximately equal height so as to facilitateattachment thereof to the lead frame.
 24. The method as recited in claim21, further comprising attaching a heat transmissive substrate to thedie/dice, the heat transmissive substrate being configured to facilitateheat flow away from the die/dice.
 25. The LED assembly as recited inclaim 21, further comprising soldering a heat transmissive substrate tothe lead frame and the die/dice via solder.